1. Technical Field The invention relates to chairs, particularly to chair backs.
2. Related Art
Office chairs with a cushion elevation mechanism and/or flexible back have been very popular. Although many chairs are provided with a flexible back with tilt flexibility, height position of the back cannot be adjusted to satisfy various users with different body length. Even if few chairs offer an adjustable back, but its structure is too complicated and its cost is too high. Complexity, adjustability and reliability are very difficult to achieve a compromise.